Patent GB-571211-A (GB)
Title: Improvements relating to machines for generating curved surfaces on articles such asglass, cams and the like
IPC: B23F23/00
Filed: 1943-05-24
Abstract: 571,211. Gear-cutting. HELLOWS GEAR SHAPER CO. May 24, 1943, No. 8261. Convention date, April 8, 1942. [Class 83 (iii)] [Also in Group XXIV] A machine for generating the teeth of gears or gear-shaped cutters, cams or other curved surfaces has a former rigidly attached to a work carrier, the former having opposite surfaces composed of curves generated from a base circle concentric with part of the carrier, and abutment surfaces inclined to each other to constitute supporting surfaces for the former in tangent relationship with the curved faces thereof. The invention is based on the principle that an involute tooth generated from a given size of base circle may be made to roll on different sized rolling circles in contact with a rack having straight-sided teeth, the pressure angle and axis of rotation being varied to suit the size of rolling circle so that the tangent to the base circle will always be perpendicular to the side of the rack tooth and will pass through the point of contact of this tooth face with the involute tooth. Thus, a cam formed of involute surfaces F<1>, F<11>, Fig. 21, generated from a base circle b<1>, c' with centre e may be made to roll on plane surfaces A, A<1> representing the sides of rack teeth on a rolling circle p<1>, c' whose centre c will travel in a straight horizontal line. To roll about a different rolling circle p<2>, c<2>, the inclinations of the surfaces A, A<1> may be altered' to the dotted line position, the centre of the base and rolling circles being thereby moved to the point e<1> and rolling will then take place about this centre with the tangent l<8>, a<8> of the base circle b<0>, c<0> perpendicular to the new surface A and passing through the point of contact X of the surface with the involute F<1>. As applied to a machine for grinding straight-toothed spurwheels, the blank 19, Fig. 1, is mounted on a spindle 18 carried by a sleeve 21 which has two involute cams 22, 23, Figs. 1 and 3, secured thereto so as to rest on flat abutments 24, 25, carried by shafts 31, 32, Figs. 3 and 4, which are rotatably adjustable by hand-operated worms 35, 36 to vary the inclinations of the surfaces 24, 25. The sleeve 21, which is vertically adjustable by means of a carriage 17 sliding on vertical guides 13, is oscillated, to cause the blank to be rolled past a stationary inclined grinding disc 16, having a flat operative face, by a worm 43 rotated through toothed and belt gearing from an electric motor 59 which is reversed at the required times by switches 62, 63, Fig. 3, and a contactor 64 driven by worm 66. The rolling motion of the sleeve 21 is guided perpendicular to its axis by a fixed bar 48 engaging a groove or rib 49 on the sleeve, and the motion is sufficient in one direction to clear the cutter 16 and allow indexing of the work spindle 18 within the sleeve. Indexing may be by hand or automatic, the hand arrangement consisting of an index plate 71, Fig. 1, attached to the spindle 18 and cooperating with a pivoted pawl carried by a strap 75 surrounding the casing 73. The pawl is rocked against a spring by a hand lever to release the plate 71, and the spindle may then be rotated by a hand wheel 70. The strap 75 may be adjusted angularly on the casing 73 by a screw 79 acting against a spring to alter the position of the pawl and give a feeding increment to the work. The grinding-disc 16 is driven by an electric or hydraulic motor mounted on a bracket which is angularly adjustable on a carriage 53 so as to vary the pressure angle of the rack teeth which it represents, the carriage 53 being laterally and longitudinally adjustable on a table 11 which is reciprocated, to traverse the disc along the teeth of the blank, by an adjustable crank 85 and connecting rod 86 driven by an electric motor. 84. In a modification, the table 11 may be dispensed with and the cutter spindle 123, Figs. 7 and 17, carried by a sleeve 138 having involute cams 139, resting on inclined abutments 141 so as to cause a linear traverse of the spindle when rotation is applied to the sleeve, in the same manner as the work spindle traverse. The sleeve is oscillated by an adjustable crank 159 and connecting rod 161 driven by an electric motor 154. The inclination of the abutments 141 may be varied equally and oppositely by right- and left-handed screws engaging their supporting shafts and the abutments, sleeve 138, and cams 139 are mounted in a carrier 165 which is rotatably adjustable in a fixed cylindrical housing 166 having its axis parallel to the spindle axis so that the direction of rectilinear movement of the cutter, such as S in Fig. 17, may be inclined for traversing along the teeth of tapered gears 170 or other tapered surfaces. Angular adjustment of the carrier 165 is effected by a worm 167 and handle 169. The cams 139 are held in contact with their abutments by the weight of the parts and by springs. The grinding cutter 122 carried by the spindle 123 rotates in a vertical plane and the inclination of the rolling path of the work 19 relatively thereto is obtained by mounting the work-spindle carrier 91, Fig. 7, together with the involute cams and abutment surfaces in a carrier 115 angularly adjustable in a cylindrical bearing 116, similar to the bearing 166, the adjustment being effected by a worm and hand wheel 124. The outer end of the work-spindle 92 is supported by a spring centre 94 mounted on an arm 93 attached to the carrier 91. The bearing 116 is vertically adjustable on a pillar 117 by a hand-operated screw 121, and the carrier 91 is oscillated by a worm driven by a hydraulic motor 105 which is reversed periodically by valves controlled from the worm in the same manner as the reversing contactor 64, Fig. 3. The work is indexed relatively to the carrier automatically by mechanism which may also be employed in the machine shown in Fig. 1, comprising a hydraulic motor 98 on an arm 97 attached to the carrier. An index plate 128, Figs. 7 and 13, is mounted on the work-spindle 92 and is engaged by a spring-pressed pawl 129 on the arm 97 having a trip arm 131. A stop 132 is adjustably mounted in a slot 135 on the stationary casing 133 which contains the worm for oscillating the carrier 115, the action being such that the trip 131 engages the stop in one direction of oscillation to remove the pawl from the plate 128, but wipes past the stop in the other direction. The motor 98 indexes the work whilst the pawl is removed from the plate. In a further modification, the grinding cutter 175, Fig. 18, has a double-sided profile equivalent to a rack tooth and is traversed along the axis of the work 19 by a cam 139 and crank 159 and rotates in a vertical stationary plane. The work-spindle carrier 91 is oscillated by the motor 105 to roll the work horizontally past the cutter in the same manner as in the machine shown in Fig. 1, the rolling mechanism being mounted on a slide 176 vertically adjustable on a pillar 117. In another modification, the cutter 177, Fig. 23, has a double-sided profile of concave involute shape and acts as a form cutter on the work 19 without rolling motion. The work-spindle 92 is indexably supported in a sleeve 178 carried by a slide 178a vertically adjustable on a pillar 117. The cutter is reciprocated along the axis of the work, either horizontally or along an inclined path as shown in Fig. 17, by the cam 139 and crank 159. An index plate 128 is attached to the spindle 92 and is engaged by a spring-pressed pawl 179, Fig. 24, carried by the arm 97. A plunger in a fluid pressure cylinder 183 carries a spring trip 185, which, on being raised engages a dog 182 attached to the pawl and releases the index plate for rotation by the fluid pressure motor 98, the trip wiping past the dog on the downward stroke. Fluid is supplied to the cylinder 183 by a pipe 192 and valve 188 which is actuated by a cam 194 on the disc of the crank 159 so that when the cutter has been moved clear of the work the pawl 179 is released from the plate 128 and the motor 98 indexes the work before the pawl can return to the next notch. The grinding cutter may be replaced by a milling or shaving cutter or by lapping or burnishing tools and the machine may produce profiled work other than gears.